Tickets can be bought from machines at underground stations and bus terminals, at tobacconists' shops, in newspaper kiosks and in some bars. They can't be bought on board the train. The most common tickets for buses, Metro, trams and local trains:
BIT, single ticket.
5BIT, multiple use ticket for five journeys.
BIG, 24-hour ticket offering an unlimited number of journeys.
CIS, weekly ticket offering an unlimited number of journeys.